As is well known to those skilled in the art, a wide variety of unsaturated charge compositions may be hydrogenated to the corresponding saturated product. Typical of these charge compositions is benzene which may be converted to cyclohexane. This process must be characterized by a high degree of activity and selectivity i.e. the benzene must be converted to cyclohexane in yields of 100%; and the product must be readily recovered in purity approaching 100% purity. This is because the cyclohexane product is to be marketed without further purification and/or distillation. Commonly it is desired that the product be of purity of 99.85% or greater cyclohexane; and the product cyclohexane should contain less than about 0.15% (1500 ppm) and preferably not more than about 0.05-0.1% (500-1000 ppm) of benzene.
It is also a feature of this process that it be flexible i.e. that it be able to selectively produce product cyclohexane over a wide range of temperature with little effect on the purity of the product.
It has been found for example that platinum-on-alumina catalysts are not sufficiently selective for use at temperatures above 500.degree. F. without some form of moderation. Typically it is found that it is necessary to have present either a volatile basic nitrogen compound or an oxide of an alkali metal such as lithium, to reduce the acidic effects of the alumina support and to thereby achieve satisfactory results at temperatures up to 650.degree. F. Successful operation at temperature above 650.degree. F. may require the use of non-acidic carbon.
It is also found that it is necessary to use a dry feed when the catalyst is alumina-based--or the low temperature reaction initiation activity is undesirably low. At temperature below about 300.degree. F., the presence of water can suppress the catalytic activity to undesirably low levels.
Although platinum-carbon has been found to be somewhat less sensitive to moisture contamination than platinum-on-alumina, the ability of such compositions to function effectively (at low platinum concentrations) as hydrogenation catalyst has not heretofore been acceptable--the performance is generally found to be inactive-to-poor; and those that are poor are found to be unreproducible.
It is an object of this invention to provide a novel catalyst system and a method of preparing the same. It is another object of this invention to provide a method for hydrogenation. Other objects will be apparent to those skilled in the art.